Hot water problem after drain down

Hi,
I've got a problem with the hot water in my house which I'd really
appreciate it if anyone could shed some light on.
Background -
House is ~20 years old and all I know about the boiler is it's a Baxi
and I think from the piping that it's a direct boiler system as the
description I found here seems to fit
http://www.diydoctor.org.uk/projects/domestic_hot_water_systems.htm#Direct%20boiler%20system :
. There's no thermostats on the system it's just time based and the
boiler runs both the Central Heating and hot water.
Problem -
I drained down the water today to have a look at a problem with a
shower valve. I did this by turning off the boiler at the control then
closing the mains water valve and running the hot and cold taps in the
bathrooms till they ran out.
After looking at the shower I opened the mains water valve and left it
to refill the tanks. Now the cold water system is working fine, but
there doesn't appear to be any hot water coming from the taps.
The central heating works fine and the pilot light on the boiler seems
lit. If I check the pipes running to the hot water tank when the hot
water is on they seem to be warm to the touch and also I've checked the
small cold water tank at the back of the hot water tank (which seems to
feed the tank) and there is water in that ok.
I'm guessing that there's something obvious that I'm missing here, so
if anyone can point me in the right direction that'd be great
Thanks
Rory

http://www.diydoctor.org.uk/projects/domestic_hot_water_systems.htm#Direct%20boiler%20system :
I'm not sure what you mean by a "direct boiler system". You will almost
certainly *not* have a direct HW cylinder - but an indirect one - like the
right-hand picture in the above reference. This has an internal coil through
which water from the boiler passes, heating the surrounding water in the
cylinder without mixing with it. Unless you have a (diabolical!) primatic
cylinder, the primary (boiler/heating coil/radiators) circuit is entirely
separate from the secondary domestic hot water circuit - each having its own
cold header tank.

Assuming that you *haven't* got a primatic system, the most likely
explanation is that you've got an air-lock in the DHW system. The classical
cure for this is to use a hosepipe to connect mains cold water to the outlet
of one of the hot taps, forcing water up into the header tank, and clearing
any trapped air in the process.
But I think we need to bottom out exactly what you *have* got, first. Any
chance that you could take a few digital photos of your installation -
particularly HW cylinder and header tank(s) - and upload them somewhere, and
post a URL here?

Thanks for the pictures. Unfortunately, nothing that I recognise!
Do you not also have a hot water cylinder in an airing cupboard? The tank
which you describe as the HW tank doesn't look very big to me, and the F&E
tank isn't where I would expect it to be, relative to the cylinder.

Those are the only tanks that I've seen whilst being in the house, and
there's definately not any other tanks that I've ever seen in any of
the rooms in the house.
One quick question. Would it be likely to cause any problems if I tried
the remedy for an airlock (putting mains water pressure into one of the
hot water taps) regardless? Just thinking it would be useful to
eliminate that as a possibility before trying other things/calling out
a plumber...
Thanks

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